The invention relates to a flap valve for controlling a gas stream, in particular an exhaust gas stream of an internal combustion engine.
In a known arrangement of a throttle valve in an exhaust gas conduit of an internal combustion engine. German Patent Disclosure DE 43 05 123 A1, the flap shaft, which carries the throttle valve and extends parallel to the plane of the flap, is guided on both sides by a bearing bore in the conduit wall of the exhaust gas conduit, and on each side protrudes through a bearing sleeve there. To achieve greater tightness while avoiding sluggishness of flap actuation, the bearing sleeves, is each axially prestressed by spring force in a respective bearing housing, are radially displaceable inside the bearing housing, and as a result dimensional deviations between stop faces for the throttle valve that are embodied on the conduit wall and the flap shaft bearing, the first time the throttle valve closes, are automatically compensated for.
The flap valve of the present invention has the advantage that as a result of the angular positioning of the flap shaft relative to the axis of the valve tube, the requisite shaft openings in the valve tube are removed from the region of the sealing face between the valve tube and the valve flap, and thus the sealing problems that occur in the known flap valves are circumvented. When the valve flap pivots, each point located on the edge of the valve flap moves along an imaginary spherical surface; thereforexe2x80x94unlike the situation with the known flap valvesxe2x80x94xe2x80x9cdrillingxe2x80x9d of singular points, with the attendant wear of the valve flap and tubular wall of the valve tube, causing leakage in the closing position of the valve flap, is prevented.
As a result of the structural design of the invention, the rotational angle of the flap shaft that is required to shift the valve flap out of its closing position to its open position and vice versa is increased. At the same time, the torque to be exerted on the flap shaft for flap adjustment is reduced. The overall result is the creation of a geometric gear whose gear ratio i is dependent on the angular positioning a of the axis of the flap shaft relative to the axis of the valve tube. If the acute angle xcex1=45xc2x0 is selected, then compared with the known flap valve, the rotational angle xcfx89 of the flap shaft for moving the valve flap between the closing position and the open position doubles to xcfx89=180xc2x0. At the same time, the torque to be exerted for the rotary motion is reduced to half that required for the known flap valves.
In an advantageous embodiment of the invention, the angle xcex1 between the flap shaft and the axis of the valve tube is chosen to be in an angular range equal to or greater than 10xc2x0 and less than 90xc2x0 and is preferably selected to be 45xc2x0. At angular values xcex1 that are less than 45xc2x0, it must be noted that then the valve flap can no longer be opened completely. However, since the characteristic curve of the gas throughput as a function of the free cross-sectional area of the valve tube has a generally strongly degressive course in flap valves, this angular range can also be utilized to achieve long rotary paths and low torques at the flap shaft.
In an advantageous embodiment of the invention, the valve tube is inserted in gastight fashion into an opening provided in the jacket of a further tube and is oriented such that the flap shaft extends perpendicularly to the axis of the further tube. Because of this structural design, exhaust gas can be supplied in metered fashion, for instance to the fresh air aspirated in the aspiration system of the internal combustion engine, if the flap valve is used as an exhaust gas recirculation valve in the intake tract of the engine; the further tube forms the air intake tube extended to the engine, and the valve tube is connected to an exhaust gas recirculation line of the engine. The disposition of the valve tube and flap shaft results in a space-saving, compact version. Alternatively, if the installation space is large enough, the valve tube can be oriented perpendicularly and the flap shaft obliquely to the axis of the air intake tube.
In a preferred embodiment of the invention, the valve tube is embodied as an elastically deformable thin-walled tube, and the valve flap is adapted in form and surface area to the inside cross section of the thin-walled tube. Because of the elastically flexible tubular wall of the thin-walled tube, a sealing element between the valve flap and the valve tube can be dispensed with, since the tubular wall, because of its elasticity, is capable of conforming tightly with the edge of the valve flap, in the closing position of the valve flap. To assure the tightness of the flap valve, of which stringent demands are made particularly when it is used as an exhaust gas recirculation valve, the form and surface area of the valve flap must be adapted exactly to the inside contour of the thin-walled tube, or must be made somewhat larger. A circular form of the inside cross section of the thin-walled tube and correspondingly a circular form of the valve flap are preferred. Alternatively, an elliptical or oval form can be considered. In the circular version, the diameter of the valve flap is dimensioned as equal to or greater than the inside diameter of the thin-walled tube. In the first case (diameter of the valve flap equal to the inside diameter of the valve tube), the valve flap is positioned relative to the flap shaft such that in the closing position of the valve flap, its surface normal is aligned with the axis of the thin-walled tube, and in the second case (diameter of the valve flap greater than the inside diameter of the valve tube), it is oriented such that in the closing position of the valve flap, its surface normal is at an acute angle to the axis of the thin-walled tube. In the latter case, in the closing position the thin-walled tube is deformed, which virtually produces an ellipse whose long radius is equivalent to the radius of the valve flap, and whose circumference is equivalent to the circumference of the tubular inside wall of the thin-walled tube.
Since upon opening of the flap valve, the thin-walled tube first deforms back again, the result for the same rotational angle of the flap shaft is initially smaller opening cross sections. By this means, better small-quantity meterability is achieved, that is, a spread of the characteristic curve of the gas throughput over the rotational angle, in the range of small rotational angles.
In an advantageous embodiment of the invention, the thin-walled tube is inserted with radial play into a rigid tubular stub and is fastened by one end to the tubular stub. As a result, the thin-walled tube is deformable freely (except in the axial direction) and can conform quite well to the valve flap and can thus achieve good sealing action. To reinforce this property, the wall thickness of the thin-walled tube must not be too great, and the diameter of the thin-walled tube must not be too small. With a view to adequate strength along with a still-tolerable vibration behavior of the thin-walled tube, a thin-walled tube diameter of 10 to 200 mm and a wall thickness of 0.05 to 2 mm have proved to be advantageous. As a result of the oblique course of the flap shaft, discontinuities in the thin-walled tube that interfere with the uniform deformability of the thin- walled tube, of the kind that can occur for instance from wall apertures for passage of the flap shaft, are also avoided.